Based on this answer from Google, http://support.google.com/webmasters/bin/answer.py?hl=en&answer=146750 you can't use the product schema if a customer has to make the purchase offline or at another retailer.
Does anyone know why they set it up this way? Has anyone ever tried to use product markup on a website when the product is purchased offline?
Also, is there another solution or another markup that would apply?
Thanks!